Why Is My Foot Swollen After Knee Surgery?

Foot and ankle swelling after knee surgery is one of the most common postoperative complaints, and it catches many patients off guard. The swelling happens because the knee sits at a critical crossroads for lymphatic drainage and blood return from the lower leg, and surgery disrupts both systems at once. Combined with reduced mobility, gravity, and the fluid load given during the procedure, the result is fluid that pools in the lowest point it can reach: your foot. While almost always a normal part of recovery, understanding why it happens and what the typical timeline looks like can help you tell the difference between expected healing and a problem that needs attention.

How Knee Surgery Sends Fluid Downhill

Your lower leg depends on a network of lymphatic vessels and veins to move fluid back up toward your heart. Most of the lymphatic drainage from the foot passes through the knee region on the inner (medial) side, near the shinbone’s upper bump. A surgical incision in this area can interrupt those lymphatic channels directly, reducing the leg’s ability to clear fluid from below the knee.¹ The longer and deeper the incision, the more drainage pathways get disrupted. This is one reason total knee replacement tends to produce more downstream swelling than a smaller arthroscopic procedure.

At the same time, the inflammatory response from surgery itself makes blood vessels in the area more permeable. Fluid that would normally stay inside capillaries leaks out into surrounding tissue. Gravity then pulls that fluid down the leg, and because your foot is the lowest point when you’re sitting or standing, that’s where it collects. After trauma or surgery, the limited transport capacity of the lymphatic system and the loss of the muscle pump both contribute to edema building up in the lower extremity.²

The “muscle pump” piece is easy to overlook. When your calf muscles contract during walking, they squeeze the deep veins and push blood upward against gravity. After knee surgery, pain, stiffness, and medical instructions to limit weight-bearing all reduce how much your calf muscles are working. Research on women with lower-limb edema has shown that when the calf muscle pump is stimulated externally, fluid pooling halts and begins to reverse, suggesting that inadequate calf muscle activity is a primary driver of the swelling many post-surgical patients experience.³ In other words, your foot swells partly because your leg isn’t moving the way it normally does.

Tourniquets and Fluid Overload During Surgery

Two factors that happen in the operating room can set the stage for more swelling before you even wake up. The first is the tourniquet. Surgeons routinely inflate a tourniquet around the upper thigh during knee procedures to create a bloodless surgical field. While this improves visibility and reduces blood loss during the operation, it temporarily starves the tissues below it of oxygen. When the tourniquet comes off and blood rushes back in, the resulting “reperfusion” triggers a burst of inflammation and oxidative stress in the limb.

Research has found a direct, positive correlation between tourniquet pressure and the degree of postoperative pain and swelling. Higher pressures cause more muscle cell damage, and the inflammatory response during reperfusion amplifies that injury.⁴ Limiting tourniquet use to only the second half of the procedure, rather than the full duration, has been shown to reduce inflammatory markers and thigh swelling compared with full-course application.⁵ A large systematic review of swelling management after total knee replacement found that avoiding or limiting tourniquet use was one of the most consistently effective strategies for reducing postoperative swelling.⁶

The second operating-room factor is intravenous fluid. During and immediately after surgery, patients typically receive a large volume of IV fluid. One observational study of patients undergoing total knee replacement found that by 24 hours after surgery, patients had received about 3,700 mL of total fluid input but only expelled about 1,980 mL, leaving roughly 1,700 mL of excess fluid retained in the body.⁷ That retained fluid has to go somewhere, and gravity directs it toward the feet and ankles. A randomized trial comparing traditional IV fluid administration with earlier transition to oral fluids found that patients who received more of their fluid by mouth had measurably less limb edema the day after surgery.⁸

The Swelling Timeline

If you’re staring at your puffy foot a few days after surgery and wondering whether this is normal, the short answer for most knee replacements is yes. A study that developed a reference chart for postoperative swelling after total knee replacement found that limb volume increases by roughly 10% per day for the first three days. Peak swelling occurs around six to eight days after surgery, and the range is wide: patients at the lower end peaked at about a 25% increase in limb volume, while those at the higher end peaked near 47%.⁹

After that peak, swelling gradually declines, though the pace varies. Many patients notice their foot and ankle are still puffier than usual at the two- or three-week mark, and mild residual swelling can linger for several months, especially after a total knee replacement. Arthroscopic procedures typically follow a shorter and milder curve because the tissue disruption is smaller. The pattern tends to be worst in the morning after a night of sleeping relatively flat and in the evening after a day of sitting with the foot down. That ebb and flow is normal and reflects how gravity and activity levels shift fluid around throughout the day.

When Foot Swelling After Knee Surgery Is a Red Flag

The vast majority of post-surgical foot swelling is harmless and resolves on its own. But a few conditions can hide behind what looks like routine edema, and knowing the warning signs matters.

Deep Vein Thrombosis

Deep vein thrombosis, or DVT, is the most serious concern. A blood clot forms in one of the deep veins of the leg, partially or fully blocking blood flow and causing the limb below it to swell. DVT affects at least 1 in every 1,000 people annually even without surgery, and the risk jumps significantly in the weeks following a lower-limb procedure because of immobility, tissue injury, and changes in blood clotting. The tricky part is that the classic signs of DVT (unilateral swelling, calf pain, warmth, and tenderness) overlap heavily with what normal post-surgical swelling looks like, so clinical signs alone are unreliable for diagnosis.¹⁰

What should prompt a call to your surgeon is swelling that suddenly gets much worse after it had been improving, new or worsening calf pain that feels deep and crampy rather than surgical-site soreness, skin that becomes noticeably red or warm compared to the other leg, or any shortness of breath or chest pain (which could indicate a clot has traveled to the lungs). Most surgical teams prescribe blood-thinning medication and compression devices after knee surgery specifically to reduce DVT risk, but clots can still occur. If anything feels off, an ultrasound can confirm or rule out a clot quickly.

Complex Regional Pain Syndrome

Complex regional pain syndrome (CRPS) is a rare but serious complication that can develop after surgery or injury. It involves dysfunction of the small nerve fibers that regulate pain, temperature, blood flow, and sweating. When those fibers malfunction, the affected limb can develop disproportionate pain, swelling, skin color changes, temperature differences, excessive sweating, and even bone loss over time.¹¹ CRPS swelling tends to look and feel different from normal postoperative edema: it’s often accompanied by burning or disproportionate pain, the skin may appear shiny or mottled, and the symptoms don’t follow the expected recovery trajectory. Early recognition and treatment are important because CRPS becomes harder to manage the longer it persists.

What Actually Helps Bring the Swelling Down

Several strategies have good evidence behind them, and most work best when combined rather than used in isolation.

Elevation and Positioning

Elevating the leg is the simplest and most universally recommended intervention. The idea is straightforward: raise the foot above the level of the heart so gravity helps fluid drain back toward the trunk rather than pooling in the ankle. Interestingly, how high you elevate may matter less than simply doing it consistently. A study of patients with ankle fractures compared high elevation (the leg propped well above the heart) with lower elevation (the leg raised but not as dramatically) and found that both groups experienced reduced swelling and pain with no significant difference between them, though patients in the high-elevation group reported more discomfort from the position itself.¹² The practical takeaway: elevate your leg whenever you’re resting, but don’t torture yourself trying to hold it at an uncomfortable angle. A pillow or two under the calf and ankle is usually enough.

Ankle Pump Exercises

Ankle pumps are one of the first exercises physical therapists teach after knee surgery, and for good reason. By flexing and extending the ankle repeatedly, you activate the calf muscle pump and push venous blood upward. A meta-analysis of randomized trials found that ankle pump exercises after lower-limb orthopedic surgery significantly improved both the speed and volume of blood flow through the leg veins, which helps prevent both swelling and blood clots.¹³ These exercises are gentle enough to start immediately after surgery, even while you’re still in bed, and they cost nothing. Doing them frequently throughout the day, rather than in one long session, keeps the pump working consistently.

Compression Devices

Pneumatic foot compression devices, sometimes called foot pumps, mimic the calf muscle pump mechanically. A randomized study found that patients who used a pneumatic foot compression system after total knee replacement had significantly less soft-tissue swelling and were able to mobilize earlier than patients who didn’t use the device.¹⁴ Another study confirmed that sequential foot compression reduced both lower-limb swelling and pain after total knee replacement, while also helping to prevent venous stasis, the sluggish blood flow that contributes to clot formation.¹⁵ Many hospitals apply these devices automatically during your stay. If you’re sent home with compression stockings instead, wearing them as directed serves a similar purpose on a smaller scale.

Ice and Cryotherapy

Applying ice or cold packs around the knee is a staple of post-surgical recovery. Cooling the tissue constricts blood vessels, reducing the leakage of fluid from capillaries into surrounding tissue and slowing the metabolic activity that fuels the inflammatory response. However, where you place the ice matters. Research using fluorescence angiography to measure skin blood flow found that placing ice directly on the surgical incision reduced blood flow by more than 40%, and that vasoconstriction persisted well after the skin had rewarmed. Placing ice on the back of the knee instead caused less of a decrease in blood flow around the incision while still providing some cooling benefit.¹⁶ The concern is that excessive blood flow reduction near the incision could slow wound healing. Most surgeons still recommend cryotherapy in the first two weeks, and a large systematic review identified it as one of the consistently effective swelling-reduction strategies, but applying it around rather than directly on the incision may be the safer approach.⁶

Knee Positioning

You might assume that keeping the knee straight after surgery is best, but evidence suggests the opposite. Maintaining the knee in a flexed position, somewhere between 30 and 90 degrees, for the first several hours to days after surgery has been consistently associated with reduced swelling.⁶ A flexed knee appears to improve venous drainage by changing the tension on the tissues around the joint. This is worth discussing with your surgical team because it cuts against the instinct to keep the leg propped straight on a pillow.

Pre-Existing Vein Problems and Swelling Risk

If you already have visible varicose veins, a history of leg swelling, or have been told you have chronic venous insufficiency (CVI), you might worry that knee surgery will make things significantly worse. The evidence here is somewhat reassuring overall but with a caveat. A study examining outcomes in patients with CVI who underwent total knee replacement found that a diagnosis of CVI was not associated with a statistically significant increase in short-term complications, long-term complications, revision surgery, or hospital readmission compared with patients without CVI. However, among patients whose CVI was classified as “complex” rather than “simple,” the odds of experiencing a complication were roughly double those of simple-CVI patients.¹⁷

What this means practically is that mild varicose veins or occasional leg swelling probably won’t change your surgical outcome or recovery trajectory much. But if you have more advanced venous disease with skin changes, chronic swelling, or a history of venous ulcers, it’s worth flagging for your surgeon. These patients may benefit from more aggressive swelling prevention during and after the procedure, and their baseline leg puffiness can make it harder to distinguish normal postoperative swelling from a developing complication.

Why the “Wrong” Leg Sometimes Swells Too

A question that comes up less often but genuinely puzzles patients: why does the non-surgical foot sometimes swell? This typically has a simpler explanation. When you’re protecting your surgical leg, you tend to sit more, stand on one leg awkwardly, and generally reduce your overall movement. Both legs lose the benefit of regular walking and calf-muscle pumping. The non-operated leg may not swell as dramatically, but some puffiness in both feet is common during recovery, especially if you spend long periods sitting in a chair or recliner with your feet below heart level.

The same fundamentals apply to managing it: elevate both legs when resting, do ankle pumps on both sides, stay as mobile as your recovery protocol allows, and stay hydrated. Dehydration can paradoxically worsen fluid retention because the body holds onto water more aggressively when intake is low. If the non-surgical leg swells suddenly or significantly more than the surgical side, that warrants medical attention because DVT can occasionally develop in either leg after surgery, not just the one that was operated on.

Medications That Affect Postoperative Swelling

Some of the medications used during and after knee surgery contribute to fluid retention independently of the surgical injury. Corticosteroids like dexamethasone are commonly given during and after total knee replacement to control nausea and reduce inflammation. While they help with pain and recovery in many ways, steroids promote sodium and water retention, adding to the fluid your body is already struggling to clear. The observational study mentioned earlier found patients received a mean cumulative dexamethasone dose of about 15 mg in the first 24 hours, contributing to the overall fluid imbalance.⁷

Some pain medications, particularly certain nonsteroidal anti-inflammatory drugs and gabapentinoids like pregabalin, can also cause peripheral edema as a side effect. If your foot swelling seems disproportionate to what your surgeon expected, reviewing your medication list is a reasonable step. On the flip side, tranexamic acid (TXA), a drug used during surgery to reduce bleeding, has been identified as one of the most consistently effective interventions for reducing postoperative swelling, particularly when given in repeated or combined regimens.⁶ TXA works by limiting blood loss and the inflammatory cascade that follows, which means less fluid escaping into the tissues in the first place. Most surgeons now use it routinely during knee replacement.